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Sakai includes a property called inactiveInterval@org.sakaiproject.tool.api.SessionManager, which dictates the length of inactive time before a users session times out. A new feature for 2.6 allows for the enabling of a session timeout warning. Session status is now checked by the Sakai portal. If the remaining session time is less than the warning time (say 10 minutes). When a session expires, the any page requests are redirected to the URL indicated by the loggedOutUrl sakai property.
To enable the session timeout warning, set the following properties in your local sakai.properties with a time interval of your choosing:
timeoutDialogEnabled=true
timeoutDialogWarningSeconds=600